Active triac triggering circuit

ABSTRACT

A power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for a triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum.

This application is a continuation of U.S. patent application Ser. No.13/868,716, filed Apr. 23, 2013. U.S. patent application Ser. No.13/868,716, filed Apr. 23, 2013, is hereby incorporated by reference.

BACKGROUND

The present disclosure pertains to thermostats and particularly tovarious kinds of power supplies for thermostats.

SUMMARY

The disclosure reveals a power supply unit for use with thermostats orother like devices requiring power. A power supply unit may be designedto keep electromagnetic interference emissions at a minimum,particularly at a level that does not violate governmental regulations.A unit may be designed so that there is enough power for triggering aswitch at about a cross over point of a waveform of input power to theunit. Power for triggering may come from a storage source rather thanline power to reduce emissions on the power line. Power for the storagesource may be provided with power stealing. Power stealing may requireswitching transistors which can generate emissions. Gate signals to thetransistors may be especially shaped to keep emissions from transistorswitching at a minimum.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 are diagrams of a thermostat power supply unit for low andhigh power, respectively;

FIGS. 3 and 4 are diagrams of a thermostat power supply having a gatedriving circuit for low and high power, respectively;

FIGS. 5 and 6 are diagrams of a thermostat power supply having an activetrigger circuit for low and high power, respectively;

FIG. 7 is a diagram of various waveforms applicable to the activetrigger circuit;

FIGS. 8 and 9 are more detailed diagrams of the thermostat power supplyfor low and high power, respectively;

FIG. 10 is a diagram of a power steal switching transistors circuit;

FIG. 11 is a diagram of an energy storage module and a linear regulator;

FIG. 12 is a diagram of a triac and an RC network;

FIG. 13 is a diagram of a half wave zero crossing detect circuit;

FIG. 14 is a diagram of a gate signal shaping circuit;

FIG. 15 is a diagram of a transistor reverse wave protection circuit;

FIG. 16 is a diagram of a negative current source;

FIG. 17 is a diagram of triac gate triggering signal source;

FIG. 18 is a diagram of triac and AC-DC converter;

FIG. 19 is a diagram of an energy storage module and a DC-DC converter;and

FIG. 20 is diagram of another half wave zero crossing detect circuit;and

FIG. 21 is a diagram of another gate signal shaping circuit.

DESCRIPTION

The present system and approach may incorporate one or more processors,computers, controllers, user interfaces, wireless and/or wireconnections, and/or the like, in an implementation described and/orshown herein.

This description may provide one or more illustrative and specificexamples or ways of implementing the present system and approach. Theremay be numerous other examples or ways of implementing the system andapproach.

A triac 12 or bypass circuit 18 and a MOSFET power steal 14 combinationmay be noted (FIG. 1). Two-wire devices may need power stealingfunctionality to supply their electronics, and conditioned triactriggering functionality to comply with FCC title 47 part 15 sub B, EMIconducted emissions regulations.

The triggering functionality need may involve using active triggeringwhich in turn requires high power in order to deliver consistent andreliable performance at a triac gate. Active triggering may be definedas the ability to store energy and supply it to trigger the triac 12near zero-crossing when a power line's energy is not sufficient.

One way of supplying high power to the electronics may be a use of aserial MOSFETs power stealing approach. Another approach may be to delaythe triac trigger, but this approach might not comply with FCCregulations.

Current transformers may also be used but they might not be able, in theload range and size available, to supply the high power requirement forthe active triac triggering and thus not comply with FCC regulations.

A thermostat device may have two states. First, the ON state 22 (FIG. 1)is when a heating demand is ON while the entire device is operating withtriac 12 ON. Second, the OFF state 23 may be when the heating demand isOFF while the device remains in operation with triac 12 OFF.

A triac 12 and MOSFET 14 combination for the ON state 22 does not appearto have been done or been used in a thermostat.

For the OFF state 23, a triac bypass circuit 18 may be needed to supplypower to thermostat electronics. Depending on power requirements, bypasscircuit 18 may be an AC-DC converter for high power such as for RFapplications, an RC (resistor-capacitor) network for moderate or lowpower, or an R (resistor) only network for rather low power.

Virtually any kind of a bypass supply approach may be used because thetriac triggering approach can be independent of the bypass supplyapproach which is not necessarily the case in a related art OFF statesupply approach of an R network with a current transformer or triactrigger being delayed.

The present thermostat topology may be a key combination for FCCcompliance. It may provide a solution for in-line line-volt thermostats.

Bypass circuit 18 may be scaled to accommodate a full range ofthermostats' energy requirements such as RF energy hungry applications(e.g., wifi, zigbee, RF host modules, and so forth), RF moderate or lowenergy applications (e.g., RF client modules, and so forth), and theusual programmable or non-programmable thermostats. Also, the triacswitch component 12 may be changed to an SCR (thyristor) or a relay withminor adjustments to circuitry.

A MOSFET gate driving circuit 28 for transition softening may be notedin FIGS. 3 and 4. Two-wire devices may need power stealing functionalityto supply their electronics. When this power stealing is done withserial MOSFETs 14, they may need to be triggered in such a way thatturning MOSFETs ON/OFF complies with FCC regulations.

By having a circuit 28 that may control the rate of charge and dischargeof the MOSFET gates, the gate switching behaviors may be controlled, andthus control the current and voltage transition generated by the powersteal module 14. Such control may enable one to reduce EMI conductedemissions.

A circuit 28 may do a positive zero crossing power steal and use twocurrent limiting devices to control the rate of charge and discharge ofthe MOSFET gates, respectively. The circuit may also use latchingcircuitry enabled by a voltage level detector, to keep the MOSFETs stateuntil the next power steal.

Some approaches may use a current transformer or the triac itself to dothe power steal. In both cases, the triac transition cannot necessarilybe controlled in such a way that will comply with FCC regulations. TheMOSFET transition may need to be smoothed. The present circuit maysoften a MOSFET transition. In this case, one may use the circuit toreduce EMI conducted emissions produced by a current zero crossing powerstealing circuit using MOSFETs.

An active triac 12 may be noted. In order to comply with FCC emissionregulations, triac triggering may need to be controlled in such a waythat EMI noise emitted on the AC main lines is kept low. Thisfunctionality may be accomplished by an active triggering.

Active triac triggering may be done with the present approach inthermostats. The approach may result in reduced EMI conducted emissionsgenerated by triac 12. Active triggering may be defined as the abilityto store energy and supply the energy to trigger triac 12 nearzero-crossing when power line's energy is not sufficient. Previously,passive triggering may have been used, which meant triggering triac 12with energy directly from a power line 13.

Active triac triggering may be done from a continuous or pulsed DCsource. Triac 12 may work in quadrants II and III. The triggering mayalso be done from an alternating continuous or pulsed DC source. Triac12 may work in quadrants I and III.

To activate the circuit, a command signal or drive 34 may be applied atan input of an active trigger circuit 33 as illustrated in FIGS. 5-7.Command signal 34 may be synchronized with the current zero crossingfrom AC line 13. The shape of an active triggering signal 36 may dependon the shape of the input command signal 34 and on the logic of activetrigger circuit 33.

For triac quadrants I and III, the practice may be to alternate the trig36 between positive and negative signals as shown by the signal profiles42 and 43. Command signal 34 may be continuous or pulsed as shown bysignal profiles 44 and 45, respectively.

For triac quadrants II and III, the practice may be to provide anegative trig signal 36 as shown by signal profiles 46 and 47. Thecommand signal 34 to active trigger circuit 33 may be continuous orpulsed as shown by signal profiles 44 and 45, respectively.

A choice of active triggering circuits may depend on the thermostatcomplexity combined with the energy consumption needed. An alternatingDC source may be more complex. Pulse triggering may consume less power.The noted active triggering approaches may reduce EMI conductedemissions produced by the triac.

FIG. 1 is a diagram of a power supply unit 11 for a thermostat needinglow power. Unit 11 may have a triac or SCR module 12 having an inputconnected to a line voltage 13. Module 12 may have a relay or sometriggerable switch. A MOSFET power steal module 14 may have an inputconnected to an output of module 12 via line 21. An output of module 14may be connected to a load voltage line 15. A source 10 may provide ACpower on line voltage 13 and line 16. Line 16 may be connected to oneend of an electric baseboard 17. Another end of baseboard 17 may beconnected to line 15.

A bypass circuit 18 may have an input connected to line voltage 13. Anoutput of circuit 18 may be a circuit low voltage line 21 connected toan input of stealing circuit 19. Unit 11 layout may be divided intothree areas including an on state area 22, an off state area 23, and analways active area 24. Modules 12 may be in area 22. Circuit 18 may bein area 23, and circuit 19 and 14 may be in area 24. A component of thetriac or SCR module 12 may be a triac. Components of the MOSFET powersteal module 14 may incorporate power steal switching MOSFETs. Acomponent of bypass circuit 18 may be an RC network. A component ofstealing circuit 19 may be for energy storage.

FIG. 2 is a diagram of a power supply unit 31 for a thermostat needingmore power like RF applications. Unit 31 may be similar to unit 11 ofFIG. 1 except that the component of circuit 18 may instead be an AC-DCconverter and the MOSFET power steal module is in the area 22.

FIG. 3 is a diagram of a power supply unit 41 for a thermostat needinglow power. Unit 41 may be similar to unit 11 of FIG. 1 except that unit41 may incorporate a zero crossing (ZC) detection module 26 in area 22.An input of module 26 may be connected to line voltage 13. An outputfrom module 26 may be a ZC signal on a line 27 to an input of a gatedriving circuit 28. Also to an input of circuit 28 may be the circuitlow voltage on line 21. An output from circuit 28 may go to an input ofmodule 14 via a line 29. Module 26 may incorporate a half wave ZC detectcomponent. Circuit 28 may incorporate a MOSFET gate signal shapingcomponent.

FIG. 4 is a diagram of a power supply unit 51 for a thermostat needinghigh power for RF applications. Unit 51 may be similar to unit 41 ofFIG. 3 except that the component of circuit 18 may instead be an AC-DCconverter and the MOSFET power steal module is in the area 22.

FIG. 5 is a diagram of a power supply unit 61 for a thermostat using lowpower. Unit 61 may be similar to unit 41 of FIG. 3 except that unit 61does not necessarily incorporate the gate driving circuit 28 and mayincorporate a microcontroller 32 and an active trigger module 33 in area22. ZC signal may go on line 27 to an input of microcontroller 32. Adrive signal on a line 34 may go to an input of active trigger module33. Stored energy may proceed from an output of circuit 19 to an inputof module 33 via a line 35. A trig signal from an output of module 33may proceed along a line 36 to an input of module 12.

FIG. 6 is a diagram of a power supply unit 71 for a thermostat needinghigh power. Unit 71 may be similar to unit 61 of FIG. 5 except that thecomponent of circuit 18 may be an AC-DC converter and the MOSFET powersteal module is in the area 22. Units 61 and 71 may be expanded toincorporate the gate driving circuit 28 arrangement of units 41 and 51.

FIG. 8 is a diagram of a low power version of a power supply unit 81having resemblances to units 11, 31, 41, 51, 61 and 71 of FIGS. 1-6,respectively. An RC network of a bypass circuit 18 may output currentalong connection 21 to power stealing switching MOSFETs. Power stealmodule 14 along connection 52 may provide stolen energy (Vrect) toenergy storage module or stealing circuit 19. A connection 53 mayprovide energy at a level (Vrect) 10 or 15 Vdc to a linear regulator andsuper cap circuit 54, the gate driving circuit of MOSFET signal shapingcircuit 28, a DC-DC negative current source 55 of active trigger module33, and a backlight circuit 56.

Regulator and super cap circuit 54 may provide 3 Vdc power alongconnection 57 to a processor and other circuits 58. Zero crossingdetector 26 having an input along connection 66 from bypass circuit 18and a half wave ZC detect of detector 26 may provide a zero crossingsignal along a connection 27 to a CPU 32. A drive signal from CPU 32along a connection 34 may go to a triac gate triggering signal circuit59 of active trigger module 33. The DC-DC negative current source 55 mayprovide energy at Vo with a current of a negative 300 mA along aconnection 61 to the triac gate triggering signal circuit 59.

A zero crossing signal may go on connection 62 from detector 26 to thegate signal shaping circuit 28. A MOSFET reverse wave protection circuit63 may have an input from line 13 and a protect signal output onconnection 64 to circuit 28.

FIG. 9 is a diagram of a high power version of a power supply unit 91which appears similar to unit 81 of FIG. 8. Line power 13 of other unitsmay be presented as two lines 1 and 2 at unit 91. Power 71 of line 1 maybe provided to power steal module 14 and MOSFET reverse wave protectioncircuit 63. Power 72 of line 2 may be provided to bypass circuit 18 andhalf wave ZC detector of circuit 26.

In contrast to unit 81, bypass circuit 18 of unit 91 may have an AC-DCconverter in lieu of an RC network. AC-DC converter may supply energy(Vrect) on connection 21 to energy storage module 19. In lieu of linearregulator and super cap circuit 54, unit 91 may have a DC-DC converter67. An output of converter 67 may be 3 Vdc to processor and circuits 58and RF Redlink™ module 68. RF Redlink™ module 68 may also be a Wifimodule or any other RF protocol. Another distinction between units 81and 91 may be connection 36 being extended as an input to gate signalshaping circuit 28.

FIGS. 10-17 are diagrams for circuitry of various parts of unit 81. FIG.10 is a diagram of power steal switching MOSFETs 14 showing a line 1,which may be of power 13 and be designated as line 71. Also, there maybe connections 29 and 52, and ground terminal 75. FIG. 11 is a diagramof energy storage module 19 and linear regulator 54. Also shown areconnections 52, 53 and 57, and ground terminal 75.

FIG. 12 is a diagram of a triac circuit 12 and an RC network of bypasscircuit 18 along with line 2, which may be of power 13 and designated asline 72. Also there may be connections 66 and 36, and ground terminal75. FIG. 13 is a diagram of a half wave ZC detect circuit 26 along withconnections Vrect 53, a connection 66, crossing connection 62, CPU ZCconnection 27, and ground terminal 75.

FIG. 14 is a diagram of the gate signal shaping circuit 28. Also shownare connections 53, 62, 64 and 29, and ground terminal 75. FIG. 15 is adiagram of a MOSFET reverse wave protection circuit 63 showingconnection 53, line 71, connection 64 for the protect signal, and aground terminal 75.

FIG. 16 is a diagram of the DC-DC negative current source 55 having anoutput on connection 61, a voltage connection 53 and a ground connection75. FIG. 17 is a diagram of triac gate triggering signal circuit 59showing a connection 61, a drive connection 34, a triac gate signalconnection 36 and a ground connection 75.

Power supply unit 91 of the high power version may be essentially thesame as power supply unit 81 of the low power version. The followingnoted Figures may reveal some differences between the units. FIG. 18 isa diagram of a high power version of bypass circuit 18 having an AC-DCconverter in lieu of an RC network as shown in FIG. 12. The AC-DCconverter may be connected to a crossing signal on connection 62, avoltage connection 53, a line 72 connection from an output of triac 12,an energy output on connection 21 and a ground connection 75. FIG. 19 isa diagram of a DC-DC converter 67 in lieu of the linear regulator ofFIG. 11. Converter 67 may have a connection 53 from the energy storagemodule 19, an output on connection 57 and a ground connection 75.

FIG. 20 is a diagram of a half wave ZC detect circuit 26 for the unit 91high power version in lieu of circuit 26 of FIG. 13. The design ofcircuit 26 in FIG. 20 may be different from circuit 26 in FIG. 13 inthat circuit 26 of FIG. 20 is designed to accommodate a line 72connection. Circuit 26 may have output lines on connection 62 and 27.Circuit 26 may have a voltage connection 53 and a ground connection 75.

FIG. 21 is a diagram of gate shaping signal circuit 28 for the unit 91high power version in lieu of circuit 28 of FIG. 14. The design ofcircuit 28 in FIG. 21 may be different from circuit 28 in FIG. 14 inthat circuit 28 of FIG. 21 is designed to accommodate a drive signal onconnection 36. Circuit 28 may also have input lines on connections 53,62 and 64. There may also be a gate signal output on connection 29.Circuit 28 may have a ground connection 75.

A thermostat power supply may incorporate a first terminal forconnection to a first line of a power source, a triac having a firstinput connected to the first terminal, a bypass circuit having a firstinput connected to the first terminal, a stealing circuit having aninput connected to an output of the bypass circuit, a power steal modulehaving an input connected to an output of the triac and an outputconnected to an output of the stealing circuit, a second terminal forconnection to a load, a zero crossing detection module having an inputconnected to the first terminal, and a gate driving circuit having aninput connected to an output of the zero crossing detection module, andan output connected to a second input of the power steal module.

The power steal module may be for stealing energy from the firstterminal. The stealing circuit may be for storing stolen energy from thepower steal module. The power steal module may incorporate one or moreMOSFETs that switch on and off for stealing energy. The gate drivingcircuit may provide gate signals to the one or more MOSFETs forswitching the one or more MOSFETs on and off.

The gate driving circuit may shape the gate signals to reduce EMIemissions from the one or more MOSFETs due to switching the one or moreMOSFETs on and off. The zero crossing detection module may provide asignal to the gate driving circuit for determining times that the gatesignals are to switch the one or more MOSFETs on and off relative to azero crossing point of a waveform on the first line of the power source.

A power unit may incorporate a first terminal for connection to a powersource, a triggerable switch having an input connected to the firstterminal, a bypass circuit having an input connected to the firstterminal, a storage having an input connected to an output of the bypasscircuit, a power steal module having an input connected to an output ofthe triggerable switch and having an output connectable to a secondterminal, a second terminal for connection to a load connected to thepower source, a zero crossing detector having an input connected to thefirst terminal, and a gate driving circuit having an input connected tothe zero crossing detector, and having an output connected to the powersteal module.

The power steal module may incorporate one or more transistors thatswitch on and off to let current flow as deemed to the second terminal.The gate driving circuit may provide signals to the one or moretransistors that switch on and off according to the signals which areadjusted in shape to result in the switch on and off of current toobtain minimized EMI emissions from switched current. The minimized EMIemissions are to comply with applicable government regulations. The oneor more transistors may be MOSFETs.

The power steal module and/or gate driving circuit may furtherincorporate MOSFETs as the one or more transistors, one or more currentlimiting devices to control a rate of charge and discharge of one ormore gates of the MOSFETs, and latching circuitry enabled by a voltagelevel detector to keep a state of the MOSFETs from a previous powersteal to a subsequent power steal.

The unit may further incorporate a MOSFET wave protection module havingan input connected to the first terminal and an output connected to aninput of the gate signal generator. The gate signal generator mayprovide the signals to the one or more transistors according to timingderived from the zero crossing detector.

A thermostat power system may incorporate a first terminal forconnection to a power supply and load arrangement, a second terminal forconnection to the power supply and load arrangement, a triggerableswitch, having an input, connected to the first terminal, a bypasscircuit having an input connected to the first terminal, an energystorage module having an input connected to an output of the bypasscircuit, a power steal module having an input connected to an output ofthe triggerable switch, and a driving circuit for a control signalhaving an output connected to a second input of the power steal module.The control signal may minimize EMI emissions from the power stealmodule.

The system may further incorporate a wave zero crossing detector havingan input connected to the first terminal and an output connected to aninput of the driving circuit.

The control signal from the driving circuit may goes to a gate of one ormore transistors to turn on or off the one or more transistors to stealpower. The turn on or off of the transistors may cause EMI emissions.The driving circuit adjusts a shape of the control signal to turn on oroff the transistors in a manner to minimize EMI emissions. The one ormore transistors may be MOSFETs.

The driving circuit may provide a control signal that is timed accordingto a signal from the wave zero crossing detector to turn on or off thetransistors in a manner to minimize EMI emissions.

The triggerable switch may be selected from a group consisting of atriac, an SCR and a relay.

The system may further incorporate a reverse wave protection modulehaving an input connected to the first terminal and an output connectedto a second input of the driving circuit.

A power supply unit for a heating, ventilation and air conditioningthermostat, may incorporate a first terminal for connection to a line ofa power source, a second terminal for connection to a load, a bypasscircuit having an input connected to the first terminal, a triac havingan input connected to the first terminal, a stealing circuit having aninput connected to an output of the bypass circuit and having an outputconnected to the second terminal, a power steal module having an inputconnected to an output of the triac, and a trigger circuit having anoutput connected to a second input of the triac.

The unit may further incorporate a zero crossing detection circuithaving an input connected to the first terminal and an output connectedto an input of the trigger circuit.

The unit may further incorporate a zero crossing detection circuithaving an input connected to the first terminal, and an interfacecircuit having an input connected to an output of the zero crossingdetection circuit and having an output connected to an input of thetrigger circuit.

A second output of the stealing circuit may be connected to a secondinput of the trigger circuit. An output of the trigger circuit may beconnected to a second input of the triac. The stealing circuit mayincorporate energy storage. Stored energy may go from the second outputof the stealing circuit to the second input of the triac.

A zero crossing signal may go from the zero crossing detection circuitto the input of the interface circuit. A zero crossing drive signal maygo from the output of the interface circuit to the input of the triggercircuit.

The zero crossing detection circuit may incorporate a half wave zerocrossing detector. The trigger circuit may incorporate a DC-DC negativecurrent source having an input connected to the second output of thestealing circuit, and a triac gate triggering signal circuit having aninput connected to an output of the DC-DC negative current source.

The unit may further incorporate a DC-DC converter connected to thesecond output of the stealing circuit. The bypass circuit mayincorporate an AC-DC converter.

The unit may further incorporate a linear regulator connected to thesecond output of the stealing circuit. The bypass circuit mayincorporate an RC network.

A power system for thermostats, may incorporate a first terminalconnected to a line of a power supply, a bypass circuit having an inputconnected to the first terminal, a triggerable switch having an inputconnected to the first terminal, a power steal module having an inputconnected to an output of the bypass circuit, a zero crossover detectorhaving an input connected to an output of the bypass circuit, a energystorage module having an input connected to an output of the power stealmodule, and a trigger circuit having an input connected to an output ofa zero crossover detector and having an output connected to a secondinput of the triggerable switch.

The trigger circuit may incorporate a processor. The processor may havean input connected to the output of the zero crossover detector and anoutput connected to the second input of the triggerable switch. Theprocessor may determine a drive signal for the triggerable switch from azero crossing signal of the output of the zero crossover detector andfrom a set of instructions.

Power may be taken from the energy storage module and used to triggerthe triggerable switch near a zero crossing of energy on the line of thepower supply as effected by the processor and a line pattern accordingto a working quadrant of the triggerable switch.

The system may further incorporate a gate signal shaper having an inputconnected to an output of the zero crossover detector and having anoutput connected to the power steal module. The power steal module mayincorporate one or more MOSFETs.

An output of the gate signal shaper may be a gate signal having a shapethat switches the one or more MOSFETs on or off in a manner to minimizeEMI emissions from switching stolen power by the one or more MOSFETs.

The system may further incorporate a MOSFET reverse wave protectioncircuit having an input connected to the first terminal and an outputconnected to a second input of the gate signal shaper.

The power steal module may steal power from the first terminal or anoutput of the bypass circuit. The power steal module may provide stolenpower to the energy storage module.

A thermostat power system may incorporate a triggerable switch having aninput connected to a first terminal, a bypass circuit having an inputconnected to the first terminal, an energy storage module having aninput connected to an output of the bypass circuit and an outputconnected to a second terminal, a power steal circuit having an inputconnected to an output of the triggerable switch, and an active triggermodule having an input connected to an output of a wave positiondetector, having an output connected to the triggerable switch, andhaving an input connected to a second output of the energy storagemodule. The first terminal and second terminal may be for connection toan AC power line and load arrangement.

The power steal circuit may incorporate transistors. A trig signal maybe sent at certain times, according to information at the output of thewave position detector, from the output of the active trigger module toa second input of the triggerable switch. A signal from the output ofthe triggerable switch to the input of the power steal circuit may turnthe transistors on or off. The active trigger module may take energy atthe second input from the second output of the energy storage to triggerthe triggerable switch near a zero crossing of the power line whenenergy directly from the power line is insufficient to trigger thetriggerable switch.

A power supply unit for a heat, ventilation and air conditioningthermostat, may incorporate a triac having an input, a gate and anoutput, a bypass circuit having an input connected to the input of thetriac, a stealing circuit having an input connected to an output of thebypass circuit, and a MOSFET power steal module having an inputconnected to the output of the triac. The input of the triac and anoutput of the MOSFET power steal module may be primary terminals forconnection in a power circuit.

The power circuit may incorporate a power source connected in serieswith an electrical load. The electrical load may be an electric heatingmechanism.

The stealing circuit may incorporate an energy storage module. TheMOSFET power steal module may steal energy and the energy may go to theenergy storage module. The energy may be used to trigger the triac at azero crossing of line voltage from the power source.

The unit may further incorporate a gate signal shaper connected to theMOSFET power steal module. The gate signal shaper may provide a gatesignal that results in a soft transition of turning on and off of theMOSFETs.

The unit may further incorporate a half wave zero cross detect moduleconnected to the line voltage, to a gate signal shaper, and to a triacgate triggering module.

Power supply electronics for a thermostat, may incorporate a firstterminal for connection to a first line of a power source, a bypasscircuit having an input connected to the first terminal, a triac havingan input connected to the first terminal, a second terminal forconnection to a load, a stealing circuit having an input connected to anoutput of the bypass circuit and an output connected to the secondterminal, and a power steal module having an input connected to theoutput of the triac and an output connected to the second terminal.

The power steal module may incorporate one or more MOSFETs that areswitched on to steal power. The stealing circuit may incorporate anenergy storage unit. Stolen power goes to the energy storage unit.

The bypass circuit may incorporate an RC network, or an AC-DC converter.

The electronics may further incorporate a linear regulator and a supercapacitor connected to an output of the energy storage unit.

The electronics may further incorporate a DC-DC converter connected toan output of the energy storage unit.

If the power steal module incorporates two or more MOSFETs, then aserial MOSFETs power stealing approach may be effected.

A thermostatic power supply may incorporate a bypass circuit, a firstterminal for connection to a power source, a second terminal forconnection to a load, a bypass circuit having an input connected to thefirst terminal, an energy storage module having an input connected tothe bypass circuit and an output connected to the second terminal, atriggerable switch having an input connected to the first terminal, anda power steal module having an input connected to an output of thetriggerable switch and an output connected to the second terminal.

The supply may further incorporate a DC-DC converter having an inputconnected to the output of the energy storage module. The bypass circuitmay incorporate an AC-DC converter.

The supply may further incorporate a linear regulator having an inputconnected to the output of the energy storage module. The bypass circuitmay incorporate an RC network.

The supply may further incorporate a super capacitor connected to thelinear regulator. The triggerable switch may be selected from a groupconsisting of a triac, SCR and a relay. The power steal module mayincorporate one or more switching MOSFETs.

In the present specification, some of the matter may be of ahypothetical or prophetic nature although stated in another manner ortense.

Although the present system and/or approach has been described withrespect to at least one illustrative example, many variations andmodifications will become apparent to those skilled in the art uponreading the specification. It is therefore the intention that theappended claims be interpreted as broadly as possible in view of therelated art to include all such variations and modifications.

What is claimed is:
 1. A power supply unit for a heating, ventilationand air conditioning thermostat, comprising: a first terminal forconnection to a line of a power source; a second terminal for connectionto a load; a bypass circuit having an input connected to the firstterminal; a triac having an input connected to the first terminal; astealing circuit having an input connected to an output of the bypasscircuit and having an output connected to the second terminal; a powersteal module having an input connected to an output of the triac; and adrive circuit having an output connected to a second input of the powersteal module.
 2. The unit of claim 1, further comprising a zero crossingdetection circuit having an input connected to the first terminal and anoutput connected to an input of the drive circuit.
 3. The unit of claim1, further comprising: a zero crossing detection circuit having an inputconnected to the first terminal; and the zero crossing detection circuithaving an output connected to a central processing unit (CPU).
 4. Theunit of claim 1, wherein a second output of the stealing circuit isconnected to a second input of the drive circuit.
 5. The unit of claim4, wherein: the stealing circuit comprises an energy storage; and storedenergy goes from the second output of the stealing circuit to the secondinput of the drive circuit.
 6. The unit of claim 5, wherein the energystorage is always active.
 7. The unit of claim 1, further comprising atrigger circuit having an output connected to an input of the drivecircuit.
 8. The unit of claim 1, further comprising: a zero crossingdetection circuit having a half wave zero crossing detector; and atrigger circuit comprising: a DC-DC negative current source having aninput connected to a second output of the stealing circuit; and a triacgate triggering signal circuit having an input connected to an output ofthe DC-DC negative current source.
 9. The unit of claim 1, furthercomprising: a DC-DC converter connected to the output of the stealingcircuit; and wherein the bypass circuit comprises an AC-DC converter.10. A power system for thermostats, comprising: a first terminalconnected to a line of a power supply; a bypass circuit having an inputconnected to the first terminal; a triggerable switch having an inputconnected to the first terminal; a power steal module having a firstinput connected to an output of the bypass circuit and a second inputconnected to the first terminal, the power steal module is configured tosteal power from the bypass circuit or the first terminal; an energystorage module having an input connected to an output of the power stealmodule for receiving stolen power from the power steal module; and aprocessor having an input connected to an output of the energy storagemodule and having an output connected to a second input of thetriggerable switch.
 11. The system of claim 10, wherein the power stealmodule is configured to be active when a thermostat is in an on stateand when the thermostat is in an off state.
 12. The system of claim 10,wherein the power steal module is configured to be active when athermostat is in an on state and inactive when the thermostat is in anoff state.
 13. The system of claim 10, further comprising: a zerocrossover detector having an input connected to an output of the bypasscircuit and an output connected to an input of the processor; andwherein the processor determines a drive signal for the triggerableswitch from a zero crossing signal of the output of the zero crossoverdetector and from a set of instructions.
 14. The system of claim 13,wherein power is taken from the energy storage module and used totrigger the triggerable switch near a zero crossing of energy on theline of the power supply as effected by the processor and a line patternaccording to a working quadrant of the triggerable switch.
 15. Thesystem of claim 13, further comprising: a gate signal shaper having aninput connected to an output of the zero crossover detector and havingan output connected to the power steal module; and wherein the powersteal module comprises one or more MOSFETs.
 16. The system of claim 15,wherein an output of the gate signal shaper is a gate signal having ashape that switches the one or more MOSFETs on or off in a manner tominimize EMI emissions from switching stolen power by the one or moreMOSFETs.
 17. The system of claim 15, further comprising a MOSFET reversewave protection circuit having an input connected to the first terminaland an output connected to a second input of the gate signal shaper. 18.A thermostat power system comprising: a triggerable switch having aninput connected to a first terminal; a bypass circuit having an inputconnected to the first terminal; an energy storage module having aninput connected to an output of the bypass circuit and an outputconnected to a second terminal; a power steal circuit having an inputconnected to an output of the triggerable switch; and an active triggermodule having an output connected to the triggerable switch and an inputconnected to a second output of the energy storage module for takingenergy from the energy storage module to trigger the triggerable switch.19. The system of claim 18, wherein the first terminal and secondterminal are for connection to an AC power line and load arrangement.20. The system of claim 18, further comprising: a wave position detectorhaving an output connected a second input of the active trigger module;and wherein: a trig signal is sent at certain times, according toinformation at the output of the wave position detector, from the outputof the active trigger module to a second input of the triggerableswitch; a signal from the output of the triggerable switch to the inputof the power steal circuit turns the power steal circuit on off; and theactive trigger module takes energy at a second input from the secondoutput of the energy storage module to trigger the triggerable switchnear a zero crossing of a power line in communication with the firstterminal and the second terminal when energy directly from the powerline is insufficient to trigger the triggerable switch.